The gypsum bandage for fixing extremities has existed for a long time. This bandage is formed by sedimentation of gypsum powder onto a cotton gauze. It is cast and hardened after impregnating with water. However, there are a series of drawbacks existing in the plaster bandage, such as bulkiness, a tendency to crack, poor air permeability, softening or breaking by soaking in water, and poor penetration of X-rays. Furthermore, the X-ray examination is taken after the patient has been fitted with the plaster bandage, and so, the condition of the fracture can't be observed clearly.
In order to overcome these drawbacks of plaster bandages, bandages prepared from high-molecular weight synthetic materials instead of plaster have been used.
U.S. Pat. Nos. 3,421,501 and 3,881,473 disclose that the substrate of a bandage is made of soft fibers. It is impregnated with a type of light-sensitive resin on its surface which can be solidified by means of ultraviolet light. But bulky hardening equipment is required; the operation is very inconvenient; and at the same time, the time required for solidification and conforming the bandage to the body part is too long. These drawbacks are a large limitation to practical usage.
U.S. Pat. No. 4,105,025 discloses a kind of thermoplastic bandage composed of high molecular weight materials. When the bandage is heated above its melting point of 77.degree.-82.degree. C., it can be wound, thereby surrounding the therapeutic position of the patient, and then it can solidify after cooling. Of course, it can be seen that the patient's skin has to withstand this temperature during winding, and the burning of the skin can be very severe.
In recent times, U.S. Pat. Nos. 4,376,438; 4,502,479, 4,427,002 and Faming Zhuanli (Chinese Patent Applications) CN 89103603,2 disclose subsequently applying aqua-activated polyurethane prepolymer as the material for an orthopedic bandage. The major components of this prepolymer are the reaction products of isocyanate and polyhydric alcohol. The method for application of this bandage is the same as that of the plaster bandage.
It can be bandaged on a patient's extremity after it is impregnated with water. The prepolymer can be polymerized when combining with water, i.e., the polymer is solidified to a rigid state, thus fixing it to the patient. In order to make the bandage solidify or harden quickly in about 10 minutes, it is necessary to blend in a certain amount of catalyst.
U.S. Pat. No. 4,376,438 discloses that aminopolyhydric alcohol is used as a catalyst. U.S. Pat. No. 4,427,002 discloses A-99, i.e., bis-(2-dimethylamino ethyl) ether, as a catalyst for controlling the time of solidification. U.S. Pat. No. 4,502,479 discloses that DMEA (dimethyl ethanol amine) or the mixture of DMEA and A-99, i.e., bis-(2-dimethylamino ethyl) ether, can be used as catalyst. Faming Zhuanli CN 89103603,2 discloses a mixture of DMEA and anhydrous K.sub.2 CO.sub.3 can be used as a mixed catalytic system.
However, the tertiary amine catalyst presented within the polyurethane bandage as above incurs gelatinizing side reactions in the prepolymer. These side reactions may form biuret or ureido formate and a small amount of trimer of isocyanate. The gelatin caused by these side reactions can cause the bandage to solidify or harden prematurely before use. Thus, the storage period of the bandage is too short and its stability is poor. Generally, the storage period of the bandage is only about 12 months at ambient temperature (23.degree. C.), and those bandages can't be made commercially available. Although many catalysts have been used to catalyze the reaction of the isocyanate moiety of polyurethane prepolymer with water, there is little use for them in the orthopedic bandage of the casting type because these catalysts can,t provide a long storage period for the orthopedic bandage.
U.S. Pat. No. 4,433,680 (Johnson & Johnson, Inc.) discloses the catalyst DMDEE, i.e., bis-(2-morpholino diethyl) ether, applied previously to the forming of polyurethane foams (U.S. Pat. No. 3,645,925) and to the forming of polyurethane injection molding elastomer (U.S. Pat. No. 4,273,885). It is used polyurethane prepolymer in the orthopedic bandage. Not only is the storage period of the bandage prolonged, but there is excellent time of solidification. Thus, this modification develops an excellent prospect for wide application of the aqua-activated polyurethane bandage.
Thereafter, U.S. Pat. No. 4,574,793 (Hexcel Co.) applied bis-(2,6-dimethylmorpholinoethyl) ether and U.S. Pat. No. 4,705,840 (3M & Co.) synthesized by itself MEMP, i.e., 4[2-methyl-2-(4-morpholino ethoxy)-ethane-] morpholine, and used it as the catalyst of the polyurethane prepolymer in the orthopedic bandage. The same effect occurred, i.e., the storage period was prolonged and satisfactory results were obtained.